MolGen Final - Mod 1
Terms in this set (63)
Describe the difference between homologous chromosomes and sister chromatids.
Homologous chromosomes are pairs of two chromosomes that code for the same genes, one from each parent. The sister chromatids are the two arms of a single chromosome that are genetically indentical.
Describe the differences between dominance, co-dominance, and incomplete dominance.
Dominance- one form a gene, or the dominant allele, is completely expressed in the phenotype and the other recessive allele is not expressed at all.
Co-dominance-both alleles are expressed equally in the phenotype, such as blood type AB.
Incomplete dominance- neither allele is dominant, a new phenotype is developed that is in between the two allelic forms of the gene, for example pink colored flowers with red and white parents.
A couple has one girl and is expecting a second child. What is the probability that this child will be a boy? After several years and several births, this couple now has six daughters and is expecting a seventh. What is the probability that this child will be a boy?
the probability of having a boy as the second child is 1/2.
after seven children, the probability of having a boy is still 1/2.
What are three of the characteristics of an autosomal dominant trait observed in a pedigree analysis?
1. effects males and females equally
2. Affected individuals all have an affected parent
3. If either one of the parents are homozygous dominant, all of the children will be affected
4. If one parent is not affected and the other is heterozygous, the child will have 1/2 probability of being affected
"The occurrence of partial expressivity and incomplete penetrance demonstrates that gene expression can be influenced by biological or environmental context." Explain this statement and give examples to support it.
Genetically speaking, brown eyes (B-) are dominant to blue eyes (bb). However, an individual can wear colored contacts in order to change his or her eye phenotype. Suppose a man with blue eyes (bb) marries a woman who appears to have blue eyes and together they have five children. Listed below are three possible outcomes. For each of the outcomes, predict the woman's genotype.
__ All five children have blue eyes.
__ All five children have brown eyes.
__ Three children have blue eyes and two have brown eyes
__1__ All five children have blue eyes.
__3__All five children have brown eyes.
__2__Three children have blue eyes and two have brown eyes
1.The woman naturally has blue eyes (bb).
2.The woman naturally has brown eyes and is heterozygous for the trait (Bb).
3.The woman naturally has brown eyes and is homozygous for the trait (BB).
Two- and three-factor testcrosses can both be used to _____________ and _____________.
b,d. map gene loci and determine genotype
In G1 of the cell cycle, the genus Ooompa lumpa has a DNA content of 2.5 picograms. Following DNA synthesis (in G2 of the cell cycle) what will be the DNA content (in picograms) of the Oompa lumpa cell?
What inheritance is suggested?
Extensive pedigree analysis on a characteristic shows all of the following:
• the characteristic affects males and females equally.
• two unaffected parents can have an affected child.
• in families in which the parents are unaffected but the children are affected, 1/4 of the children are affected.
List in order of occurrence the phases of mitosis:
Albinism, lack of pigmentation in humans, results from an autosomal recessive gene (a). Two parents with normal pigmentation have an albino child. What is the probability that their next three children will be albino?
Where on the chromatid are the microtubules attached?
An organism has a haploid number of 6. How many possible assortments of chromosomes are possible based on the independent assortement of the chromosomes?
When Thomas Hunt Morgan crossed his red-eyed F1generation flies to each other, the F2generation included both red- and white-eyed flies. Remarkably, all the white-eyed flies were male. What was the explanation for this result?
The gene involved is on the X chromosome
Codominant alleles are expressed in individuals that are _______________.
In the following tetrahybrid cross AaBbCcDd x AaBbCcDd what proportion of the F2 offspring would be expected to be phenotypically ABCD ?
The expected ratio of phenotypes among the progeny of a test cross is 1:1:1:1. Out of 200 total resulting progeny, 48 occur in one of the four phenotypic classes. Given this information, which of the following must also be true?
The value of observed - expected for this cell= -2
Round (R) seed shape is dominant to wrinkled (r) seed shape in pea plants. If an RR plant is crossed with an rr plant, what is the frequency of phenotypes in the F2 generation?
3 round seeds, 1 wrinkled seed
A situation where there are more than two alternative forms of a given gene would be called ________.
A condition in which one gene pair masks the expression of a nonallelic gene pair is called ________.
Assume that a dihybrid cross is made in which the genes' loci are autosomal, independently assorting, and incompletely dominant. How many different phenotypes are expected in the offspring?
Polydactyly is expressed when an individual has extra fingers and/or toes. Assume that a man with six fingers on each hand and six toes on each foot marries a woman with a normal number of digits. Having extra digits is caused by a dominant allele. The couple has a son with normal hands and feet, but the couple's second child has extra digits. What is the probability that their next child will have polydactyly?
A recessive allele in tigers causes the white tiger. If two normally pigmented tigers are mated and produce a white offspring, what percentage of their remaining offspring would be expected to have normal pigmentation?
Name the single individual whose work in the mid-1800s contributed to our understanding of the particulate nature of inheritance as well as the basic genetic transmission patterns. With what organism did this person work?
Gregor Mendel, Pisum Sativum
Drosophila melanogaster, the fruit fly, has a 2n chromosome number of 8. Assuming that a somatic G2 nucleus contains about 8.0 picograms of DNA, how many picograms of nuclear DNA would you expect in:
a) Mitotic metaphase
b) a primary oocyte (metaphase)
c) a secondary oocyte (metaphae)
d) a first polar body (metaphase)
a-d: 8, 8, 4, 4
What types of phenotypic ratios are likely to occur in crosses when dealing with a single gene pair where all the genotypic combinations are of equal viability?
Typical ratios resulting from epistatic interactions in dihybrid crosses would be ________.
(*add up to16)
List two differences and two similarities between mitosis and meiosis.
Interactions among the human ABO blood group alleles involve _______ and ________.
(c,e) complete dominance and co-dominance
Name one characteristic of X-linkage that is often used to identify X-linked genes in pedigree analysis.
Criss-cross pattern of inheritance-where all sons exhibit mutant mother phenotype, the phenotype largely or exclusively affects males.
Chromosomes are in unseparated, sister-chromatid form, at the end of which phase(s)?
a. Meiosis I prophase
b. Meiosis I anaphase
c. Meiosis II prophase
d. Meiosis II anaphase
e. Mitosis prophase
f. Mitosis anaphase
a. meiosis I prophase, b. meiosis I anaphase, c. meiosis II prophase, e. mitosis prophase
What does this pedigree analysis on a characteristic indicate:
•only males are affected.
•affected fathers always pass the trait to sons.
List four terms used to describe the normal morphologies, with respect to arm ratio, of eukaryotic chromosomes.
If they live long enough, the penetrance of individuals carrying the Huntington's Disease allele will be what?
In the following tetrahybrid cross AaBbCcDd x AaBbCcDd what proportion of the F2 offspring would be expected to be genotypically AaBbCcDd ?
Embryonic stem cells are the subject of a great deal of research. What characteristic of embryonic stems cells accounts for this scientific interest?
they are potentially totipotent
In order to determine if mutations from different organisms that exhibit the same phenotype are allelic, which test would you perform?
Often, a mutation in a gene results in a reduction of the product of that gene. The term given for this type of mutation is:
loss-of-function or null (in the case of complete loss)
Assume that a cross is made between AaBb and aabb plants and that all the offspring are either AaBb or aabb. These results are consistent with the following circumstance:
Assume that a black guinea pig crossed with an albino guinea pig produced 5 black offspring. When the albino was crossed with a second black one, 4 black and 3 albino offspring were produced. What genetic explanation would apply to these data?
Describe the difference between meiosis I and meiosis II.
Meiosis I - reduction division because the number of chromosomes per cell is reduced by half. Also, homologous pairs separate.
Meiosis II - equational division and sister chromatids separate.
What are three of the characteristics of an autosomal recessive trait that are observed in a pedigree analysis?
1.neither parent has to display the trait
2.the trait may be passed sons or daughters in equal proportions.
3.in cases where the trait is passed it only occurs 1/4 of the time.
How do incomplete penetrance and variable expressivity differ?
Incomplete penetrance means that an individual with the affected genotype does not always express the expected
phenotype. Whereas, varible expressivity means that individuals that are affected can show a varying degree the severity of
the trait (ex: Down Syndrome individuals can be very sever or highly functional).
Which modes of inheritance are influenced by the sex of individuals. Select all that apply.
Sex limited, y-linked, x-linked
Assume that the somatic cells of a male contain one pair of homologous chromosomes (e.g., A1 and A2), and an additional chromosome without a homolog (e.g., W). What chromosomal combinations would be expected in the meiotic products (spermatids) of a single primary spermatocyte? (There may be more than one answer.)
1. A1,W + A1,W + A2 + A2
2.A1 + A1 + A2,W + A2,W
An allele is
an alternate form of a gene
Ability to roll the tongue is caused by a dominant allele. A woman is a "roller," but one of her parents is not.
What is the woman's genotype?
In the following cross, what proportion of individuals will have the Bombay phenotype?
AB Hh x AB Hh
3/4 or 1/4??
In a healthy male, how many sperm cells would be expected to be formed from (a) 400 primary spermatocytes? (b) 400 secondary spermatocytes?
a) 1600, b) 800
The Chi-square test involves a statistical comparison between measured (observed) and predicted (expected) values. One generally determines degrees of freedom as
one less than the number of classes being compared
During interphase of the cell cycle,
DNA content essentially doubles
Extensive pedigree analysis on a characteristic shows all the following:
• if a woman with an affected father has children with an unaffected man, half of the sons and none of the daughters
• affected females always have an affected father and an affected maternal grandfather.
• the trait is never passed from father to son.
What mode of inheritance is suggested?
Which are abnormalities involving numbers of X chromosomes?
[ ] Down syndrome
[ ] Huntington's disease
[x] Klinefelter syndrome
[x] XXXX syndrome
[x] Turner syndrome
Albinism, lack of pigmentation in humans, results from an autosomal recessive gene (a). Two parents with normal pigmentation
have an albino child. What is the probability that their next child will be an albino girl?
Genes come in different versions called
If a pair of homologous chromosomes fails to separate during anaphase of meiosis I, what will be the
chromosome number of the four resulting gametes with respect to the normal haploid number (n)?
n+1; n+1; n-1: n-1
Human blood types are an example of codominance because:
The A and B alleles both express equally in individuals with both alleles
If a couple with Sickle cell disease genotypes Ss and Ss mate and have one child with the disease, what is the
chance the next child has the disease as well?
The stage at which "sister chromatids go to opposite poles" immediately follows which stage listed below?
In the G0 stage of the cell cycle, which of the following is true:
the cell exits the cell cycle
the formation of two cells at the end of mitosis in both plants and animals
Which of the following parental genotypes will produce only heterozygous F1 offspring?
AA x aa
Assume that a cross is made between AaBb and aabb plants and that the offspring fall into approximately equal numbers of the following groups: AaBb, Aabb, aaBb, aabb. These results are consistent with the following circumstance: